The enhancement mechanism of SO2 removal by the presence of NO2 under low temperature and humid conditions was studied in a fixed bed reactor system. The presence of NO2 in the flue gas can enhance SO2 removal. The interaction between SO2 and NO2 in gas phase could not explain the effect of NO2 on SO2 removal under lowtemperature and humid conditions. When Ca(NO3)2 and Ca(NO2)2 as additive were added on the surface of sorbent, the desulfurization activity of sorbent decreased. However, the sorbent pretreated by NO2 for a moment has higher SO2 removal. The oxidization of SO32^(-) to SO42^(-) and the evolution of sorbent surface structure in the presence of NO2 can explain the enhancement of SO2 removal by the presence of NO2. HSO3^(-) and SO3^(-) reacted with NO2 to form sulfate, which can accelerate the hydrolysis of SO2. The reaction between NO2 and Ca(OH)2 can make the unreacted sorbet under the SO2 removal product exposed to the reactant gas.